Primary: wisdom Secondary: intelligence Tertiary: charisma
This skill is automatically in use.
Imitating animal's pack tactics shapeshifters have learned to fight perfectly with other shapeshifters in the same form as they are. Although being loners by nature, shapeshifters seem to be able to work together very well. For example while in a form of a wolf they are able to work together like real wolves would. So by knowing each other's tactics and moves perfectly they are able to deliver astonishing attacks upon their foe without actually even communicating to each other. For this reason these attacks come as an surprise to their opponents.
You can see pack tactics that are available for you with the guild command.